Ni-base directionally solidified superalloy and Ni-base single crystal superalloy

ABSTRACT

A Ni-base directionally solidified superalloy and a Ni-base single-crystal superalloy, which have superior creep strength at a high temperature, consists essentially of from 5.0 percent by weight to 7.0 percent by weight of Al, from 4.0 percent by weight to 16.0 percent by weight of Ta+Nb+Ti, from 1.0 percent by weight to 4.5 percent by weight of Mo, from 4.0 percent by weight to 8.0 percent by weight of W, from 3.0 percent by weight to 8.0 percent by weight of Re, 2.0 percent by weight or less of Hf, 10.0 percent by weight or less of Cr, 15.0 percent by weight or less of Co, from 1.0 percent by weight to 4.0 percent by weight of Ru, 0.2 percent by weight or less of C, 0.03 percent by weight or less of B, and Ni and inescapable impurities as a balance. The superalloys can be used for a turbine blade, a turbine vane and the like of a jet engine, an industrial gas turbine and the like.

TECHNICAL FIELD

The present invention relates to a Ni-base directionally solidifiedsuperalloy and a Bi-base single crystal superalloy. More particularly,the present invention relates to a new Ni-base directionally solidifiedsuperalloy and a new Ni-base single-crystal superalloy, both of whichhave a superior creep property at high temperatures and are suitablecandidates to be used in components which are used at a high temperatureand in a highly stressed state, such as a turbine blade and a turbinevane of, for example, a jet engine and a gas turbine.

BACKGROUND ART

Conventionally, a Ni-base directionally solidified superalloy and aNi-base single-crystal superalloy have been known as a Ni basesuperalloy. For example, Rene80 (an alloy consisting essentially of 9.5percent by weight of Co, 14.0 percent by weight of Cr, 4.0 percent byweight of Mo, 4.0 percent by weight of W, 3.0 percent by weight of Al,17.0 percent by weight of Co, 0.015 percent by weight of B, 5.0 percentby weight of Ti, 0.03 percent by weight of Zr, and Ni as a balance), andMar-M247 (an alloy consisting essentially of 10.0 percent by weight ofCo, 8.5 percent by weight of Cr, 0.65 percent by weight of Mo, 10.0percent by weight of W, 5.6 percent by weight of Al, 3.0 percent byweight of Ta, 1.4 percent by weight of Hf, 0.16 percent by weight of C,0.015 percent by weight of B, 1.0 percent by weight of Ti, 0.04 percentby weight of Zr, and Ni as a balance) have been known as a directionallysolidified superalloy. Moreover, TMD-103 (Japanese Patent No. 2,905,473)has been known as a third generation Ni-base directionally solidifiedsuperalloy.

These conventional Ni-base directionally solidified superalloys isinferior in strength at high temperatures to a Ni-base single-crystalalloy, but they are good in manufacturing yield due to less occurrencesof grain misorientation and less cracking at casting and excellent in apoint that complex heat treatment is not required. However, strength ofa Ni-base directionally solidified superalloy has been required to beimproved for practical use. Moreover, a Ni-base directionally solidifiedsuperalloy in strength at a high temperature has been desired becauserise of turbine inlet temperature is the most efficient in order toimprove efficiency of a gas turbine.

Similarly, a Ni-base single-crystal superalloy with further excellentstrength at a high temperature has been also desired, though a Ni-basesingle-crystal superalloy, which is produced by casting, has superiorstrength at a high temperature.

DISCLOSURE OF THE INVENTION

In order to solve the above-mentioned problems, a first aspect of thepresent invention is to provide a Ni-base directionally solidifiedsuperalloy consisting essentially of from 5.0 percent by weight to 7.0percent by weight of Al, from 4.0 percent by weight to 16.0 percent byweight of Ta+Nb+Ti, from 1.0 percent by weight to 4.5 percent by weightof Mo, from 4.0 percent by weight to 8.0 percent by weight of W, from3.0 percent by weight to 8.0 percent by weight of Re, 2.0 percent byweight or less of Hf, 10.0 percent by weight or less of Cr, 15.0 percentby weight or less of Co, from 1.0 percent by weight to 4.0 percent byweight of Ru, 0.2 percent by weight or less of C, 0.03 percent by weightor less of B and Ni and inevitable impurities as a balance. According toa second aspect of the present invention, there is provided a Ni-basedirectionally solidified superalloy including from 2.8 percent by weightto 4.5 percent by weight of Mo in the above-mentioned composition.According to a third aspect of the present invention, there is provideda Ni-base directionally solidified superalloy including from 4.0 percentby weight to 6.0 percent by weight of Ta in the above-mentionedcomposition. According to a fourth aspect of the present invention,there is provided a Ni-base directionally solidified superalloyconsisting essentially of from 5.8 percent by weight to 6.0 percent byweight of Al, from 5.5 percent by weight to 6.5 percent by weight ofTa+Nb+Ti, from 2.8 percent by weight to 3.0 percent by weight of Mo,from 5.5 percent by weight to 6.5 percent by weight of W, from 4.8percent by weight to 5.0 percent by weight of Re, from 0.08 percent byweight to 0.12 percent by weight of Hf, from 2.0 percent by weight to5.0 percent by weight of Cr, from 5.5 percent by weight to 6.0 percentby weight of Co, from 1.8 percent by weight to 2.2 percent by weight ofRu, from 0.05 percent by weight to 0.1 percent by weight of C, from 0.01percent by weight to 0.02 percent by weight of B, and Ni and inevitableimpurities as a balance.

According to a fifth aspect of the invention, there is provided aNi-base directionally solidified superalloy including from 0.01 percentby weight to 0.1 percent by weight of Si in the above-describedcompositions. According to a sixth aspect of the invention, there isprovided a Ni-base directionally solidified superalloy further includingone or more elements selected from the group consisting of 2.0 percentby weight or less of V, 1.0 percent by weight or less of Zr, 0.2 percentby weight or less of Y, 0.2 percent by weight or less of La, and 0.2percent by weight or less of Ce in the above-mentioned compositions.

Moreover, a seventh aspect of the present invention is to provide aNi-base single-crystal superalloy consisting essentially of from 5.0percent by weight to 7.0 percent by weight of Al, from 4.0 percent byweight to 16.0 percent by weight of Ta+Nb+Ti, from 1.0 percent by weightto 4.5 percent by weight of Mo, from 4.0 percent by weight to 8.0percent by weight of W, from 3.0 percent by weight to 8.0 percent byweight of Re, 2.0 percent by weight or less of Hf, 10.0 percent byweight or less of Cr, 15.0 percent by weight or less of Co, from 1.0percent by weight to 4.0 percent by weigh of Ru, 0.2 percent by weightor less of C, 0.03 percent by weight or less of B, and Ni and inevitableimpurities as a balance. According to an eighth aspect of the presentinvention, there is provided a Ni-base single-crystal superalloyincluding from 2.8 percent by weight to 4.5 percent by weight of Mo inthe above-mentioned composition. According to a ninth aspect of thepresent invention, there is provided a Ni-base single-crystal superalloyincluding from 4.0 percent by weight to 6.0 percent by weight of Ta inthe above-mentioned compositions. According to a tenth aspect of thepresent invention, there is provided a Ni-base single-crystal superalloyconsisting essentially of from 5.8 percent by weight to 6.0 percent byweight of Al, from 5.5 percent by weight to 6.5 percent by weight ofTa+Nb+Ti, from 2.8 percent by weight to 3.0 percent by weight of Mo,from 5.5 percent by weight to 6.5 percent by weight of W, from 4.8percent by weight to 5.0 percent by weight of Re, from 0.08 percent byweight to 0.12 percent by weight of Hf, from 2.0 percent by weight to5.0 percent by weight of Cr, from 5.5 percent by weight to 6.0 percentby weight of Co, from 1.8 percent by weight to 2.2 percent by weight ofRu, from 0.05 percent by weight to 0.1 percent by weight of C, from 0.01percent by weight to 0.02 percent by weight of B, and Ni and inevitableimpurities as a balance.

Furthermore, an eleventh aspect of the present invention is to provide aNi-base single-crystal superalloy including from 0.01 percent by weightto 0.1 percent by weight of Si in the above-mentioned compositions.According to a twelfth aspect of the invention, there is provided aNi-base single-crystal superalloy including one or more elementsselected from the group consisting of 2.0 percent by weight or less ofV, 1.0 percent by weight or less of Zr, 0.2 percent by weight or less ofY, 0.2 percent by weight or less of La, and 0.2 percent by weight orless of Ce in the above-mentioned compositions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing results of creep tests for a Ni-basedirectionally solidified superalloy according to EXAMPLE 1 and for aconventional one, using the Larson-Miller parameters.

FIG. 2 is a view showing results of creep tests for a Ni-basedirectionally solidified superalloy according to EXAMPLE 2 and aconventional one, using the Larson-Miller parameters.

Here, symbols in the drawings are defined as follows:

-   -   A TMD-103 (a third generation Ni-base directionally solidified        superalloy);    -   B Mar-M247 (a commercial Ni-base directionally solidified        superalloy); and    -   C Rene80 (a commercial Ni-base directionally solidified        superalloy).

FIG. 3 is a schematic view of a casting apparatus and a method toproduce a Ni-base directionally solidified superalloy and a Ni-basesingle-crystal superalloy according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention provides a Ni-base directionally solidifiedsuperalloy and a Ni-base single-crystal superalloy with theabove-mentioned features. Embodiments of the invention will beexplained.

A Ni-base directionally solidified superalloy and a Ni-base singlecrystal superalloy have a γ phase (matrix) as an austenite phase and aγ′ phase (precipitated phase) as an intermediate phase which isprecipitated and dispersed in the parent phase. The γ′ phase consistsessentially of an intermetallic compound represented by Ni₃Al and theexistence of the γ′ phase improves strength at a high temperature of aNi-base directionally solidified superalloy and a Ni-base single crystalsuperalloy.

The reason for limiting compositions of a Ni-base directionallysolidified superalloy and a Ni-base single crystal superalloy of thepresent invention will be explained as follows.

Cr is an element with excellent oxidation resistance to improve thecorrosion resistance at a high temperature. Cr (chromium) is effectivefor further improving the oxidation resistance and can be added to 10percent by weight by adjusting addition of Ru. The content of Cr ispreferably 10.0 percent by weight or less, and, most preferably, from2.0 percent by weight to 5.0 percent by weight. It is not preferablethat Cr is not contained, because desired corrosion resistance at a hightemperature cannot be obtained. It is not preferable that in the casewhere the content of Cr exceeds 10.0 percent by weight, precipitation ofγ′ phase is suppressed and a harmful phase such as a σ phase and μ phaseis formed to decrease strength at a high temperature.

Mo (molybdenum) is dissolved into a y matrix under coexistence of W andTa to increase strength at a high temperature, and contributes tostrength at a high temperature by precipitation hardening. The contentof Mo is preferably from 1.0 percent by weight to 4.5 percent by weight,more preferably, from 2.8 percent by weight to 4.5 percent by weight,and, most preferably, from 2.8 percent by weight to 3.0 percent byweight. It is not preferable that in the case where the content of Mo isless than 1.0 percent by weight, desired strength at a high temperaturecannot be obtained. Moreover, it is not preferable that in the casewhere the content of Mo exceeds 4.5 percent by weight, not only strengthat a high temperature is reduced but also corrosion resistance at a hightemperature is reduced.

W (tungsten) improves strength at a high temperature by solid solutionstrengthening and precipitation hardening under coexistence of Mo andTa. The content of W is preferably from 4.0 percent by weight to 8.0percent by weight, and, most preferably, from 5.5 percent by weight to6.5 percent by weight. It is not preferable that in the case where thecontent of W is less than 4.0 percent by weight, desired strength at ahigh temperature cannot be obtained. It is not preferable that in thecase where the content of W exceeds 8.0 percent by weight, corrosionresistance at a high temperature is reduced.

Ta (tantalum), Nb (niobium), and Ti (titanium) improves strength at ahigh temperature by solid solution strengthening and precipitationstrengthening under coexistence of Mo and W. Moreover, some of themimproves high temperature strength by forming precipitates in the γ′phase. The content of Ta+Nb+Ti is up to 16 percent by weight byadjusting each component, preferably, from 4.0 percent by weight to 16.0percent by weight. The content is more preferably from 4.0 percent byweight to 10.0 percent by weight, and, most preferably, from 5.5 percentby weight to 6.5 percent by weight. It is not preferable that in thecase where the content of Ta+Nb+Ti is less than 4.0 percent by weight,desired strength at a high temperature cannot be obtained. It is notpreferable that in the case where the content of Ta+Nb+Ti exceeds 16.0percent by weight, a harmful phase such as a σ phase and a μ phase isformed to decrease strength at a high temperature.

Al (aluminum) combines with Ni (nickel) to form an intermetalliccompound represented by Ni₃Al. Finely and uniformly dispersed γ′precipitates are composed of this intermetallic compound. The formationof an alloy with these γ′ phase with a volume fraction of from 60% to70% results in an improvement in strength at high temperatures. Thecontent of Al is preferably from 5.0 percent by weight to 7.0 percent byweight, and, most preferably, from 5.8 percent by weight to 6.0 percentby weight. It is not preferable that in the case where the content of Alis less than 5.0 percent by weight, a precipitated amount of the γ′phase becomes not enough and desired strength at a high temperaturecannot be obtained. It is not also preferable that in the case where thecontent of Al exceeds 7.0 percent by weight, many of coarse γ phasescalled as an eutectic γ′ phase are formed to make performing solutionheat treatment impossible and high strength at a high temperature cannotbe obtained.

Hf (hafnium) is a grain boundary segregation element which is segregatedat a grain boundary between a γ phase and a γ′ phase to strengthen theboundary. Thereby, strength at a high temperature is improved. Thecontent of Hf is preferably 2.0 percent by weight or less and, morepreferably, from 0.08 percent by weight to 0.12 percent by weight. It isnot preferable that in the case where Hf is not contained, a grainboundary is not sufficiently strengthened and therefore desired strengthat a high temperature cannot be obtained. It is not also preferable thatin the case where the content of Hf exceeds 2.0 percent by weight, thereis a possibility that local melting is caused to decrease strength at ahigh temperature.

Co (cobalt) raises a solid solution limit of Al, Ta and the like into aparent phase under a high temperature and causes a fine γ′ phase to beprecipitated and dispersed by heat treating. Thereby, strength at a hightemperature is improved. The content of Co is preferably 15.0 percent byweight or less and, more preferably, from 5.5 percent by weight to 6.0percent by weight. It is not preferable that in the case where Co is notcontained, a precipitated amount of a γ′ phase becomes not enough andtherefore desired strength at a high temperature cannot be obtained. Itis not also preferable that in the case where the content of Co exceeds15.0 percent by weight, balance between Co and other elements such asAl, Ta, Mo, W, Hf and Cr is lost to cause a harmful phase to beprecipitated and strength at a high temperature is decreased.

Re (rhenium) is dissolved into a γ phase of a parent phase to improvestrength at a high temperature by solid solution strengthening.Corrosion resistance is also improved. On the other hand, addition of alarge amount of Re causes strength at a high temperature to bedecreased, because a TCP phase, which is a harmful phase, isprecipitated at a high temperature. Re can be added up to 8 percent byweight by adjusting the addition amount of Ru. The content of Re ispreferably from 3.0 percent by weight to 8.0 percent by weight and, morepreferably, from 4.8 percent by weight to 5.0 percent by weight. It isnot preferable that in the case where the content of Re is less than 3.0percent by weight, solid solution strengthening of a γ phase becomes notenough and desired strength at a high temperature cannot be obtained. Itis not also preferable that in the case where the content of Re exceeds6.0 percent by weight, a TCP phase is precipitated at a high temperatureand high strength at a high temperature can not be obtained.

Ru is one of elements which characterize the present invention andsuppresses precipitation of a TCP phase to improve strength at a hightemperature. The content of Ru is preferably from 1.0 percent by weightto 4.0 percent by weight and, more preferably, from 1.8 percent byweight to 2.2 percent by weight. It is not preferable that in the casewhere the content of Ru is less than 1.0 percent by weight, a TCP phaseis precipitated at a high temperature and high strength at a hightemperature cannot be obtained. It is not also preferable that in thecase where the content of Ru exceeds 4.0 percent by weight, cost ishigh.

C (carbon) contributes to strengthening of a grain boundary. The contentof C is preferably 0.2 percent by weight and or less, more preferably,from 0.05 percent by weight to 0.1 percent by weight. It is notpreferable that in the case where C is not contained, an effect ofstrengthening of a grain boundary cannot be obtained. It is not alsopreferable that in the case where the content of C exceeds 0.2 percentby weight, ductility is deteriorated.

B (boron) contributes to strengthening of a grain boundary in a similarmanner to that of C. The content of B is preferably 0.03 percent byweight or less and, more preferably, from 0.01 percent by weight to 0.02percent by weight. It is not preferable that in the case where thecontent of B is less than 0.01 percent by weight, an effect ofstrengthening of a grain boundary cannot be obtained. It is not alsopreferable that in the case where the content of B exceeds 0.03 percentby weight, ductility is deteriorated.

Si (silicon) is an element which forms an SiO₂ film on a surface of analloy as a protective film to improve oxidation resistance. Thoughsilicon has been treated as an impurity element so far, silicon isintentionally contained and is effectively used for improving oxidationresistance in present invention. Moreover, it is considered that crackshardly occur in the SiO₂ film in comparison with other protective oxidefilms and the SiO₂ film has an effect to improve creep and fatigueproperties. However, the content of silicon has been limited to from0.01 percent by weight to 0.1 percent by weight, because addition of alarge amount of silicon lowers solid solution limits of other elements.

In a Ni-base directionally solidified superalloy and a Ni-basesingle-crystal superalloy according to the present invention, at leastone of V, Zr, Y, La, or Ce is added to the composition.

V (vanadium) is an element which is dissolved into a γ′ phase andstrengthens a γ′ phase. However, the content of V is limited to 2.0percent by weight or less because excessive addition of V decreasescreep strength.

Zr (zirconium) is an element which strengthens a grain boundary in asimilar manner to that of B and C. However, the content of Zr is limitedto 1.0 percent by weight or less because excessive addition of Zrdecreases creep strength.

Each of Y (yttrium), La (lanthanum), and Ce (cerium) is an element whichimproves adhesiveness of the film that forms protective oxide film, suchas alumina and chromia, during high heat operations. However, thecontents of Y, La, and Ce are limited to 0.2 percent by weight or less,respectively, because excessive addition of them lowers solid solutionlimits of other elements.

A Ni-base directionally solidified superalloy and a Ni-basesingle-crystal superalloy according to the present invention can beproduced as a product with a composition of predetermined elements bycasting, considering procedures and conditions of a well-known process.The attached drawing of FIG. 3 is an outline view illustrating a processfor a directionally solidified superalloy (DS) and a single crystalsuperalloy. It is seen from FIG. 3 that a single crystal superalloy is amodification of a directionally solidified superalloy. That is, a metaland an alloy produced by casting usually have a polycrystallinestructure in which crystals are disposed in all directions. Adirectionally solidified alloy is composed of a cluster of slendercrystalline grains, called as a columnar crystal, an orientation ofwhich is arranged in a loading direction. A single crystal alloy isobtained as an extension of a directionally solidified alloy byselecting one of the columnar crystals for growth. Accordingly, a singlecrystal alloy also has a structure in which an orientation of crystalsis arranged in a loading direction. A single crystal alloy is producedby an apparatus shown at the right of FIG. 3. The apparatus is differentfrom an apparatus, which is shown at the left of FIG. 3, for adirectionally solidified alloy only in a point that a selector forselecting a crystal is provided. Both of the apparatuses are same,except the above point.

A Ni-base single-crystal superalloy can be obtained as a single crystalby using a selector for growing one crystal in production of a Ni-basedirectionally solidified superalloy.

Hereinafter, examples will be shown for further detailed explanation. Itis obvious that the present invention is not limited to the followingexamples.

EXAMPLES Example 1

A cast of a directionally solidified alloy, which consists of 5.8percent by weight of Co, 2.9 percent by weight of Cr, 2.9 percent byweight of Mo, 5.8 percent by weight of W, 5.8 percent by weight of Al,5.8 percent by weight of Ta, 0.10 percent by weight of Hf, 4.9 percentby weight of Re, 2.0 percent by weight of Ru, 0.07 percent by weight ofC, 0.015 percent by weight of B, and Ni and inevitable impurities as abalance was obtained by melting and casting with a solidification rateof 200 mm/h in a vacuum. Cylindrical test pieces (Nos. 1 and 2) with adiameter of 4 mm and a length of 20 mm were made from the cast of adirectionally solidified alloy and creep tests were conducted accordingto conditions shown in TABLE 1. Pieces of data with regard to rupturelife, elongation, and reduction are shown in TABLE 1.

Moreover, values of the Larson-Miller parameter were calculatedaccording to the following formula and are shown in TABLE 1.LMP=T(20+log (tr))×10⁻³

where T: Kelvin temperatures, and tr: Rupture life in hours. A relationbetween an LMP value and a stress is shown in FIG. 1 in comparison withthat of existing TMD-103.

A in the drawing represents a case of the TMD-103. In FIG. 1, anupper-left portion represents results at a low temperature and under ahigh stress and a lower-right portion represents results at a hightemperature and under a low stress. When a curve is situated in a rightside, creep strength is higher.

It is obvious from FIG. 1 that a Ni-base directionally solidifiedsuperalloy according to EXAMPLE 1 is superior in creep strength at ahigh temperature.

Example 2

After preheating of a cast of a directionally solidified alloy which hasbeen obtained in a similar manner to that of EXAMPLE 1 was conducted ata temperature of 1300° C. for one hour in a vacuum, solution heattreatment was performed. That is, the cast was heated to 1320° C., wasmaintained at the temperature for five hours and then was cooled by air.After the above step, two-step aging treatment was conducted. That is,as a first step, the cast was maintained at 1100° C. for four hours in avacuum and then was cooled by air. Subsequently, as a second step, thecast was maintained at 870° C. for twenty hours in a vacuum and then aircooling was executed.

Test pieces (Nos. 3 to 5) were made in a similar manner to that ofEXAMPLE 1 and creep tests were conducted according to conditions shownin TABLE 1. Pieces of data with regard to life, elongation, andreduction are shown in TABLE 1. LMP values are shown in TABLE 1 and FIG.2.

It is seen from FIG. 1 that the Ni-base directionally solidifiedsuperalloy according to EXAMPLE 2 is superior in creep strength to thatof EXAMPLE 1.

Further, it is understood from FIG. 2 that the Ni-base directionallysolidified superalloy according to EXAMPLE 2 is remarkably moreexcellent in creep strength over a wide range of temperatures incomparison with commercial Ni-base directionally solidified superalloys,Rene80 (C) and Mar-M247 (B).

Example 3

It was confirmed that creep strength of a single crystal superalloy witha similar composition to that of EXAMPLE 1 was superior to that ofEXAMPLE 2 because life of the superalloy according to EXAMPLE 3 wasimproved two or three times longer than that in EXAMPLE 2.

INDUSTRIAL APPLICABILITY

A Ni-base directionally solidified superalloy according to the presentinvention, containing a Ru element, is an alloy with more improved creepstrength at further higher temperatures in comparison with that of athird-generation Ni-base directionally solidified superalloy which doesnot contain a Ru element. Accordingly, when the superalloy according tothe present invention is used for a turbine blade, a turbine vane andthe like in a jet engine, an industrial gas turbine and the like, theycan be used in combustion gas at a higher temperature.

Moreover, a Ni-base single-crystal superalloy according to the presentinvention is superior in strength at a high temperature and has improvedcasting properties and good manufacturing yield.

TABLE 1 Test LMP piece Temperature Stress Life Elongation Reduction P =20 (No.) (° C.) (kgf/mm2) (h) (%) (%) (×1000) 1 900 40 310.6 13.4 14.326.387 2 1100 14 85.3 16.7 37.8 30.114 3 900 40 402.2 10.1 15.1 26.519 41000 25 152.5 14.9 15.9 28.243 5 1100 14 126.3 14.9 26.3 30.349

1. A Ni-base directionally solidified superalloy consisting essentiallyof from 5.0 percent by weight to 7.0 percent by weight of Al, from 4.0percent by weight to 16.0 percent by weight of Ta+Nb+Ti, wherein Ta isfrom 4.0 percent by weight to 5.8 percent by weight, from 1.0 percent byweight to 4.5 percent by weight of Mo, from 4.0 percent by weight to 8.0percent by weight of W, from 3.0 percent by weight to 8.0 percent byweight of Re, 2.0 percent by weight or less of Hf, 10.0 percent byweight or less of Cr, 15.0 percent by weight or less of Co, from 1.0percent by weight to 4.0 percent by weight of Ru, from 0.07 percent byweight to 0.2 percent by weight of C, from 0.015 percent by weight to0.03 percent by weight of B, and Ni, and inevitable impurities as abalance.
 2. The Ni-base directionally solidified superalloy as claimedin claim 1, wherein the superalloy includes from 2.8 percent by weightto 4.5 percent by weight of Mo.
 3. The Ni-base directionally solidifiedsuperalloy as claimed in claim 1, wherein the super alloy consistsessentially of from 5.8 percent by weight to 6.0 percent by weight ofAl, from 5.5 percent by weight to 6.5 percent by weight of Ta+Nb+Ti,from 2.8 percent by weight to 3.0 percent by weight of Mo, from 5.5percent by weight to 6.5 percent by weight of W, from 4.8 percent byweight to 5.0 percent by weight of Re, from 0.08 percent by weight to0.12 percent by weight of Hf, from 2.0 percent by weight to 5.0 percentby weight of Cr, from 5.5 percent by weight to 6.0 percent by weight ofCo, from 1.8 percent by weight to 2.2 percent by weight of Ru, from 0.07percent by weight to 0.015 percent by weight of C, from 0.01 percent byweight to 0.02 percent by weight of B, and Ni and inevitable impuritiesas a balance.
 4. The Ni-base directionally solidified superalloy asclaimed in any one of claims 1, 2 or 3, wherein the super alloy includesfrom 0.01 percent by weight to 0.1 percent by weight of Si.
 5. TheNi-base directionally solidified superalloy as claimed in claim 4,wherein the superalloy includes one or more elements selected from thegroup consisting of 2.0 percent by weight or less of V, 1.0 percent byweight or less of Zr, 0.2 percent by weight or less of Y, 0.2 percent byweight or less of La, and 0.2 percent by weight or less of Ce.
 6. TheNi-base directionally solidified superalloy as claimed in any one ofclaims 1, 2, or 3, wherein the superalloy includes one or more elementsselected from the group consisting of 2.0 percent by weight or less ofV, 1.0 percent by weight or less of Zr, 0.2 percent by weight or less ofY, 0.2 percent by weight or less of La, and 0.2 percent by weight orless of Ce.
 7. A Ni-base single-crystal superalloy consistingessentially of from 5.0 percent by weight to 7.0 percent by weight ofAl, from 4.0 percent by weight to 16.0 percent by weight of Ta+Nb+Tiwherein Ta is from 4.0 percent by weight to 5.8 percent by weight, from1.0 percent by weight to 4.5 percent by weight of Mo, from 4.0 percentby weight to 8.0 percent by weight of W, from 3.0 percent by weight to8.0 percent by weight of Re, 2.0 percent by weight or less of Hf, 10.0percent by weight or less of Cr, 15.0 percent by weight or less of Co,from 1.0 percent by weight to 4.0 percent by weigh of Ru, from 0.07percent by weight to 0.2 percent by weight of C, from 0.015 percent byweight to 0.02 percent by weight of B, and Ni and inevitable impuritiesas a balance.
 8. The Ni-base single-crystal superalloy as claimed inclaim 7, wherein the superalloy includes from 2.8 percent by weight to4.5 percent by weight of Mo.
 9. The Ni-base single-crystal superalloy asclaimed in claim 7, wherein the superalloy consists essentially of from5.8 percent by weight to 6.0 percent by weight of Al, from 5.5 percentby weight to 6.5 percent by weight of Ta+Nb+Ti, from 2.8 percent byweight to 3.0 percent by weight of Mo, from 5.5 percent by weight to 6.5percent by weight of W, from 4.8 percent by weight to 5.0 percent byweight of Re, from 0.08 percent by weight to 0.12 percent by weight ofHf, from 2.0 percent by weight to 5.0 percent by weight of Cr, from 5.5percent by weight to 6.0 percent by weight of Co, from 1.8 percent byweight to 2.2 percent by weight of Ru, from 0.07 percent by weight to0.015 percent by weight of C, from 0.01 percent by weight to 0.02percent by weight of B, and Ni and inevitable impurities as a balance.10. The Ni-base single-crystal superalloy as claimed in claim 7, 8 or 9,wherein the superalloy includes one or more elements selected from thegroup consisting of 2.0 percent by weight or less of V, 1.0 percent byweight or less of Zr, 0.2 percent by weight or less of Y, 0.2 percent byweight or less of La, and 0.2 percent by weight or less of Ce.
 11. TheNi-base single-crystal superalloy as claimed in claim 7, wherein thesuperalloy includes from 0.01 percent by weight to 0.1 percent by weightof Si.
 12. The Ni-base single-crystal superalloy as claimed in claim 11,wherein the superalloy includes one or more elements selected from thegroup consisting of 2.0 percent by weight or less of V, 1.0 percent byweight or less of Zr, 0.2 percent by weight or less of Y, 0.2 percent byweight or less of La, and 0.2 percent by weight or less of Ce.